A new world benchmark for hydraulic skidding was established this June in Geoje-Si, South Korea, with the loadout of the 19,400t deck for an Arctic class semisubmersible destined eventually to serve on Russia’s Shtokman gas field. David Morgan reports.
The recent loadout of the first of two Gazflot topsides from a Korean yard not only gave Dutch heavy transportation specialist Dockwise the chance to hone its floatover skills, but also provided a challenging debut for heavy lift specialist ALE’s new skid shoes.
The topsides are for two drilling/ production semis ordered by Gazprom for its giant Shtokman gas field development in the Barents Sea (OE April 2009).
ALE was contracted to lift the 19,400t topsides and skid them onto the semisubmersible transportation vessel Black Marlin, which would then move to an offshore location for Dockwise to take care of hull and deck mating using the ‘floating floatover’ technique (OE August). Loadout of the second topsides, scheduled for October, will follow the same procedure.
The ALE heavy-duty skid system employed for this project incorporated the new 650t skid shoes unveiled recently by the company’s design team in Breda, the Netherlands. Secured by a strong box construction in the top of the housing to provide strength and stability, the skid shoes are hydraulically driven by 83t capacity push-pull units to slide over Teflon blocks in the skid track, with the load on the skid shoes supported by hydraulic cylinders. The cylinders from each of the skid shoes are hydraulically connected to create either a 3- or 4-point suspension system designed to support the load without overstressing.
The first of the Gazflot topsides was lifted and transported using both 650t and 500t capacity skid shoes, the system comprising 24 of each, all integrated with hydraulic jacks to control the load.
‘The lifting and loadout of the topside required different loadings at various support points, which necessitated a high level of engineering,’ says ALE project engineer Sjak Aerts. ‘This, coupled with the heavy loads involved, made it an ideal initial project for the new additions to our skid system, as we needed the higher capacities of the new skid shoes combined with the control provided by the hydraulic cylinders.’
The hydraulic cylinders were retracted during the installation of the skid shoes under the platform. Once all 48 skid shoes were in place they were hydraulically connected to provide a 3-point hydraulic supporting system to lift the topside from its supports – both the 650t and 500t hydraulic cylinders had a 450mm out of a maximum 600mm stroke for lifting the 19,400t load clear of the grillage on the vessel.
The topside was then moved to the quayside and subsequently moved on to the Black Marlin using 24 push-pull units, eight link beams and over 1000m of skid track. It then travelled a total distance of 82m on eight skid lanes. Once in position, the load was lowered and set down on the heavy cargo vessel’s grillages using the hydraulic cylinders, and the skid shoes were uncoupled and removed.
The integrated push-pull system avoids large horizontal load in to the quayside, vessel and fenders, explains Aerts. Combined with the specially developed ‘hinged’ link beams, the system allows the vessel to move freely, ensuring tide and ballasting motions can be accurately monitored.
‘The topside was skidded on the vessel within 10 hours and the whole project went without a hitch,’ says Sjak.
‘The new skid shoes have proved to be perfect for the job and we’re looking forward to moving the second topside in October.’ OE